1. Field of the Invention
The present invention relates to an apparatus for thermally developing a thermally developable photosensitive material. More particularly, the present invention pertains to a thermal developing apparatus for use in thermally developing an image recorded by exposure on a photosensitive material.
2. Description of the Related Art
A typical thermally developable photosensitive material (hereinafter referred to simply as a "photosensitive material") has a photosensitive layer and an electrically conductive, heat-generating layer. An image recorded on the photosensitive layer by exposure is developed by heating the photosensitive layer by means of the Joule heat generated by supplying a heating current through the electrically conductive, heat-generating layer. To obtain a desired degree of development of the image with respect to this type of photosensitive material, it is necessary to supply a heating current of a predetermined magnitude therethrough for a predetermined period of time on the basis of time-temperature data given by the manufacturer of the photosensitive material concerned.
An apparatus for heating the above-described type of photosensitive material has already been proposed wherein the heating temperature is accurately controlled by measuring the resistance value of the electrically conductive, heat-generating layer formed on the photosensitive material, utilizing the fact that this resistance value varies depending upon the temperature of the photosensitive material (see U.S. patent application Ser. No. 48,483).
However, the temperature-resistance characteristic differs depending upon the material employed for the electrically conductive, heat-generating layer, and it is therefore impossible to effect an appropriate correction with respect to a photosensitive material having an electrically conductive, heat-generating layer formed of a material other than a specific one. Further, even when a constant electric power is supplied to the electrically conductive, heat-generating layer, the temperature of the photosensitive material varies with changes in the ambient air temperature, which makes it impossible to effect an accurate temperature control.